Method and arrangement in a telecommunication system

ABSTRACT

A method in a terminal for providing an ACK/NAK message to a base station is provided. The terminal counts the number of assigned downlink subframes detected from the base station resulting in k. The terminal then establishes whether each of a number of transport blocks comprised in the counted k downlink subframes is correctly received or not. In the case when each one of the transport blocks, comprised in the k downlink subframes is estimated as correctly received the terminal provides to the base station an encoded ACK message for the k subframes, which comprises k, the number of subframes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/002,144, filed Dec. 30, 2010, pending, which claims the benefit ofU.S. Provisional Application No. 61/076,899, filed Jun. 30, 2008, whichclaims the benefit of PCT Application No. PCT/SE2008/051427, filed onDec. 9, 2008, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a method and an arrangement in a basestation and a method and an arrangement in a mobile terminal. Inparticular, it relates to the handling of a “ACK”/“NAK” message providedto the base station by the terminal.

BACKGROUND

A key requirement on Long Term Evolution (LTE) currently beingstandardized in 3GPP is frequency flexibility, and for this purposecarrier bandwidths between 1.4 MHz and 20 MHz are supported, as is bothfrequency division duplex (FDD) and time division duplex (TDD), so thatboth paired and unpaired spectrum can be used. For FDD the downlink(DL), i.e. the link from the base stations to the mobile terminals, anduplink (UL), i.e. the link from the mobile terminals to the basestations, use different frequencies and can hence transmit simultaneous.For TDD, uplink and downlink use the same frequency and cannot transmitsimultaneously. Uplink and downlink can however share the time in aflexible way, and by allocating different amounts of time, such as thenumber of subframes of a radio frame, to uplink and downlink, it ispossible to adapt to asymmetric traffic and resource needs in uplink anddownlink.

The above asymmetry also leads a significant difference between FDD andTDD. Whereas for FDD the same number of uplink and downlink subframes isavailable during a radio frame, for TDD that the number of uplink anddownlink subframes may be different. One of many consequences of this isthat in FDD a mobile terminal can always send feedback in response to aDL assignment of resources in an UL subframe subject to a certain fixedprocessing delay. In other words, every DL subframe can be associated toa specific later UL subframe for feedback generation in way that thisassociation is one-to-one, i.e. to each UL subframes is associatedexactly one DL subframe. For TDD however, since the number of UL and DLsubframes during a radio frame may be different, it is in general notpossible to construct such one-to-one association. For the typical casewith more DL subframes than UL subframes, it is rather so that feedbackfrom several DL subframes needs to be transmitted in each UL subframe.

In LTE, a radio frame of 10 ms duration is divided into ten subframes,each 1 ms long. In case of TDD, a subframe can be assigned to uplink ordownlink, i.e. uplink and downlink transmission cannot occur at the sametime. Furthermore, each 10 ms radio frame is divided into twohalf-frames of 5 ms duration where each half-frame comprises of fivesubframes.

The first subframe of a radio frame is always allocated to DLtransmission. The second subframe is a special subframe and it is splitinto three special fields, DwPTS, GP and UpPTS, with a total duration of1 ms. UpPTS is used for uplink transmission of sounding referencesignals and, if so configured, reception of a shorter random accesspreamble. No data or control signaling can be transmitted in UpPTS. GPis used to create a guard period between periods of DL and UL subframesand may be configured to have different lengths in order to avoidinterference between UL and DL and is typically chosen based on thesupported cell radius. The DwPTS field is used for downlink transmissionmuch like any other DL subframe with the difference that it has shorterduration.

Different allocations of the remaining subframes to UL and DL aresupported, both allocations with 5 ms periodicity in which the first andsecond half-frame have identical structure, and allocations with 10 msperiodicity for which the half-frames are organized differently. Forcertain configurations the entire second half-frame is assigned to DLtransmission.

In the DL of LTE, Orthogonal Frequency Division Multiplex (OFDM) with asub carrier spacing of 15 kHz is used. In the frequency dimension thesubcarriers are grouped into resource blocks, each containing twelveconsecutive subcarriers. The number of resource blocks depends on thesystem bandwidth, and the minimum bandwidth corresponds to six resourceblocks. Depending on the configured cyclic prefix length a 1 ms subframecontains either 12 or 14 OFDM symbols in time. The term resource blockis also used to refer to the two-dimensional structure of all OFDMsymbols within a subframe, times a resource block of subcarriers. Thedownlink part of the special subframe DwPTS has a variable duration, andcan assume lengths of 3, 9, 10, 11 or 12 OFDM symbols for the case withnormal cyclic prefix, and 3, 8, 9 or 10 symbols for the case withextended cyclic prefix.

In order to improve performance of transmission in both the DL and ULdirection, LTE uses Hybrid-ARQ (HARQ). The basic idea of HARQ is thatafter receiving data in a DL subframe the terminal attempts to decode itand then reports to the base station whether the decoding was successful(ACK, acknowledgement) or not (NAK, negative acknowledgement). In caseof an unsuccessful decoding attempt the base station thus receives a NAKin a later UL subframe, and can retransmit the erroneously receiveddata.

Downlink transmissions may be dynamically scheduled, i.e. in eachsubframe the base station transmits control information on whichterminals are to receive data and upon which resources in the current DLsubframe. By resources is here meant some set of resource blocks. Thecontrol signaling is transmitted in the first 1, 2 or 3 OFDM symbols ineach subframe. (For system bandwidth < or =10, it is transmitted in thefirst 2, 3 or 4 OFDM symbols in each subframe). The data sent to aterminal in a single DL subframe is often referred to a transport block.

A terminal will thus listen to the control channel, and if it detects aDL assignment addressed to itself it will try to decode the data. Itwill also generate feedback in response to the transmission, in the formof an ACK or a NAK depending on whether the data was decoded correctlyor not. Furthermore, from the control channel resources on which theassignment was transmitted by the base station, the terminal candetermine the corresponding Physical Uplink Control Channel resource(PUCCH) in case that the ACK/NACK is transmitted on the PUCCH. The PUCCHresource may also be configured by the network, which is the case when achannel quality report or a scheduling request is transmitted at thesame time as the ACK/NAK feedback is to be provided.

For LTE FDD the terminal will in response to a detected DL assignment insubframe n, send an ACK/NAK report in uplink subframe n+4. For the casewith so-called Multiple In Multiple Out (MIMO) multi-layer transmissiontwo transport blocks are transmitted in a single DL subframe, and theterminal will respond with two ACK/NAK reports in the correspondinguplink subframe.

The assignment of resources to the terminals is handled by thescheduler, which takes into account traffic and radio conditions so asto use the resources efficiently while also meeting delay and raterequirements. Scheduling and control signaling may be done on a subframeto subframe basis, i.e. each downlink subframe is scheduledindependently of others.

As described above, the first step for a terminal to receive data fromthe base station in a DL subframe is to detect a DL assignment in thecontrol field of a DL subframe. In the case that the base station sendssuch an assignment but the terminal fails to decode it, the terminaldoes obviously not know that is was scheduled and will hence not respondwith an ACK/NAK in the uplink. This situation is referred to as a missedDL assignment. If the absence of an ACK/NAK can be detected by the basestation, it can take this into account for subsequent retransmissions.Typically the base station should at least retransmit the missingpacket, but it may also adjust some other transmission parameters.

There is not a one-to-one relation between UL and DL subframes asdiscussed above. Thus the terminal cannot always send an ACK/NAK inresponse to a DL assignment in subframe n in UL subframe n+4, since thissubframe may not be allocated to UL transmission. Hence each DL subframemay be associated with a certain UL subframe subject to a minimumprocessing delay, meaning that ACK/NAKs in response to DL assignments insubframe n are reported in subframe n+k with k>3. Furthermore, if thenumber of DL subframes is larger than the number of UL subframes,ACK/NAKs in response to assignments in multiple DL subframes may need tobe sent in a single UL subframe. For a given UL subframe, the number ofassociated DL subframes depends on the allocation of subframes to UL andDL, and can be different for different UL subframes within a radioframe.

Since DL assignments can be given independently across DL subframes, aterminal may be assigned DL transmissions in multiple DL subframes thatare all to be acknowledged in a single UL subframe. Hence the uplinkcontrol signaling needs to support, in some way, feedback of ACK/NAKsfrom multiple DL transmissions from a terminal in a given UL subframe.

One obvious way to approach the above problem is to allow the terminalto transmit multiple individual (for each DL transmission) ACK/NAK bitsin a single UL subframe. Such protocols have however worse coverage thantransmission of one or two ACK/NAK reports. In addition, the moreACK/NAKs that are allowed to be transmitted from a single terminal, themore control channel resources need to be reserved in the uplink. Toimprove control signaling coverage and capacity, it has been agreed todo some form of compression, or bundling, of ACK/NAKs. This means thatall ACK/NAKs that are to be sent in a given UL subframe are combinedinto a smaller number of bits, such as a single ACK/NAK report. As anexample, the terminal can transmit an ACK only if the transport blocksof all the DL subframes were received correctly and hence to beacknowledged. In any other case, meaning that a NAK for at least one DLsubframe is to be transmitted, a combined NAK is sent for all DLsubframes.

Hence, as described above, to each UL subframe in TDD a set of DLsubframes can be associated, rather than a single subframe as in FDD,for which DL transmissions are to be given ACK/NAK response in the givenUL subframe. In the context of bundling this set is often referred to asthe bundling window. The two basic approaches then include:

-   -   Multiplexing of multiple ACK/NAKs, meaning that multiple        individual ACK/NAK reports of the subframes are fed back. For        the case with no MIMO, and a configuration with 3 DL subframes        (including DwPTS) and two UL subframes as depicted in FIG. 2 b,        up to two bits of ACK/NAK feedback is fed back in subframe #2        and #7 and one up to one bit in subframes 3 and 8. In the        general case, there may be a third state so that ACK/NACK/DTX is        fed back. DTX then represents that the terminal did not        receive/detect any assignment during in the corresponding DL        subframe.    -   Bundling of multiple ACK/NAKs, meaning that a single ACK/NAK is        generated from the individual ACK/NAKs and that this single        ACK/NAK is fed back. For the case with no MIMO, the terminal        combines the ACK/NAKs of multiple DL subframes so that a single        ACK/NAK is generated and fed back in all UL subframes.

A basic problem with ACK/NAK bundling and multiplexing is that aterminal may miss a DL assignment, which may not be indicated in thebundled response. For instance, assume that the terminal was scheduledin two consecutive DL subframes. In the first subframe the terminalmisses the scheduling assignment and will not be aware that it wasscheduled, while in the second subframe it did successfully receive thedata. The terminal will, as a result, transmit an ACK, which the basestation will assume holds for both subframes, including data in thefirst subframe the terminal was not aware of. As a result, data will belost. The lost data needs to be handled by higher-layer protocols, whichtypically takes a longer time than hybrid-ARQ retransmissions and isless efficient. In fact, a terminal will not transmit any ACK/NAK in agiven UL subframe, only if it missed every DL assignment that was sentduring the bundling/multiplexing window associated with the UL subframe.

SUMMARY

It is therefore an object of the present invention to provide a methodin a network unit, and an arrangement adapted to perform said method toimprove the detection of missed DL assignment.

According to a first aspect of the present invention, the object isachieved by a method in a terminal for providing an ACK/NAK message to abase station. The base station and the terminal are comprised in atelecommunications system. The terminal counts the number of assigneddownlink subframes detected from the base station resulting in k. Theterminal then establishes whether each of a number of transport blockscomprised in the counted k downlink subframes is correctly received ornot.

In the case when each one of the transport blocks, comprised in the kdownlink subframes is estimated as correctly received the terminalprovides to the base station an encoded ACK message for the k subframes,which comprises k, the number of subframes.

In the case when any of the transport blocks comprised in the number kdownlink subframes is estimated as not correctly received, the terminalmay provide one encoded NAK message for the k subframes bundled to thebase station.

According to a second aspect of the present invention, the object isachieved by a method in a base station for handling an ACK/NAK messagefrom a terminal. The base station and the terminal are comprised in atelecommunications system. The base station sends a number of downlinksubframes comprising transport blocks to the terminal.

In the case when each one of the transport blocks comprised in the kdownlink subframes is estimated as correctly received by the terminal,the base station receives from the terminal one encoded ACK message fork subframes. The encoded ACK message comprises k, the number ofsubframes detected by the terminal.

In the case when any of the transport blocks comprised in the number kdownlink subframes is estimated by the terminal as not correctlyreceived, the base station may receive one encoded NAK message for the ksubframes bundled from the terminal.

According to a third aspect of the present invention, the object isachieved by an arrangement in a terminal for providing an ACK/NAKmessage to a base station. The base station and the terminal arecomprised in a telecommunications system. The terminal arrangementcomprises a counting unit configured to count the number of assigneddownlink subframes detected from the base station resulting in k and anestablishing unit configured to establish whether each of a number oftransport blocks comprised in the counted k downlink subframes iscorrectly received or not. The terminal arrangement further comprises asending unit configured to provide to the base station, an encoded ACKmessage for the k subframes, which comprises k, the number of subframes,when each one of the transport blocks, comprised in the k downlinksubframes is estimated as correctly received. The sending unit mayfurther be configured to provide to the base station one encoded NAKmessage for the k subframes bundled, when any of the transport blockscomprised in the number k downlink subframes is estimated as notcorrectly received.

According to a fourth aspect of the present invention, the object isachieved by an arrangement in a base station for handling ACK/NAKmessage from a terminal: The base station and the terminal are comprisedin a telecommunications system. The base station arrangement comprises asending unit configured to send a number of downlink subframescomprising transport blocks to the terminal. The base stationarrangement further comprises a receiving unit configured to receivefrom the terminal one encoded ACK message for k subframes. The encodedACK message comprises k, the number of subframes detected by theterminal. The encoded ACK message is received when each one of thetransport blocks, comprised in the k downlink subframes is estimated ascorrectly received by the terminal. The receiving unit may further beconfigured to receive from the terminal one encoded NAK message for thek subframes bundled, when any of the transport blocks comprised in thenumber k downlink subframes is estimated by the terminal as notcorrectly received.

Since the number of received downlink subframes is transmitted when anACK is transmitted, but not when a NAK is transmitted, the base stationcan avoid, or reduce the probability for, the case that a missedassignment is interpreted as an ACK, which causes additional delays dueto higher layer retransmissions and so on. In case a NACK istransmitted, the base station can not interpret a missed assignment asbeing correctly received since it then typically assumes that at leastone subframe has not been correctly received. Furthermore, as comparedto always feeding back the number of received subframes, uplinkperformance is improved since a smaller number of different messages arepossible and hence lower uplink signalling is needed. This in turnimplies that the signalling is reduced and that the detection of misseddownlink assignment is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail with reference to attacheddrawings illustrating exemplary embodiments of the invention and inwhich:

FIG. 1 is a schematic block diagram illustrating embodiments of awireless telecommunication system.

FIG. 2 a and b are schematic block diagrams illustrating embodiments ofassociation of each downlink subframe with an uplink subframe for twodifferent UL:DL allocations.

FIG. 3 a, b and c are schematic diagrams illustrating embodiments of theinvention.

FIG. 4 a, b and c are schematic diagrams illustrating embodiments of theinvention.

FIG. 5 is schematic block diagrams illustrating embodiments of a 16QAMconstellation.

FIG. 6 is a flow chart illustrating embodiments of a method in a mobileterminal.

FIG. 7 is a schematic block diagram illustrating embodiments of a mobileterminal arrangement.

FIG. 8 is a flow chart illustrating embodiments of a method in a basestation.

FIG. 9 is a schematic block diagram illustrating embodiments of a basestation arrangement.

DETAILED DESCRIPTION

The present invention relates to a method in a terminal, and anarrangement adapted to perform said method, for providing to a basestation, such as an eNodeB, information from which the base station candetermine whether one or several assignments have been missed. Thepresent invention also relates to a method in a base station such as aneNodeB, and an arrangement adapted to perform said method, for receivingfrom a terminal, information from which the base station can determinewhether one or several assignments have been missed. The methods andarrangements may be put into practice in the embodiments describedbelow.

The problem solved is to determine if the terminal has missed anassignment and hence “forgotten” to report a bundled NAK in case ACK/NAKbundling is used. If the terminal reports a NAK, there is no problem,but if the terminal reports an ACK there is a problem since the terminalshould ideally report a NAK since of the subframes is not correctlyreceived (in fact, the terminal missed the assignment and it did noteven try to decode the data). The base station keeps tracks of thenumber of assigned subframes k′, and the base station demodulates andestimates whether the terminal reports a NAK or an any of M−1 ACKmessages (assuming that there are M constellation points). In case oneof the M−1 ACK messages is received, say ACK k, it compares k with thenumber of assigned subframes k′ and can in this way detect if theterminal missed any downlink assignment.

FIG. 1 depicts a wireless telecommunication system 100, such as e.g. theE-UTRAN, LTE, LTE-Adv, 3rd Generation Partnership Project (3GPP) WCDMAsystem, Global System for Mobile communications/Enhanced Data rate forGSM Evolution (GSM/EDGE), Wideband Code Division Multiple Access(WCDMA), Worldwide Interoperability for Microwave Access (WiMax), orUltra Mobile Broadband (UMB). The telecommunication system 100 may useTDD or FDD and comprises a base station 110 and a terminal 120 adaptedto communicate with each other over a radio channel 130. The basestation 110 may be a NodeB, an eNodeB or any other network unit capableto communicate with a terminal over a radio channel that may be a TDD orFDD radio channel. The terminal 120 may be a mobile phone, a PersonalDigital Assistant (PDA), a user equipment (UE) or any other network unitcapable to communicate with a base station over a radio channel.

The base station 110 uses HARQ and ACK/NAK bundling, at least forcertain uplink subframes, for transmitting data packets over the radiochannel 130. The data packets are transported in transport blocks withinsubframes over the radio channel 130. For this purpose, the base station110 schedules a number of subframes to be transmitted to the mobileterminal 120. If a NAK message is received from the mobile terminal 120,the base station 110 retransmits the non-acknowledged subframes untilthey have been acknowledged by the mobile terminal 120 or until a timeperiod expires, which time period may be a predetermined time period.

For a given uplink subframe, a number of downlink subframes, denoted K,transmitted from the base station 110 to the terminal 120 is associated.In some embodiments, a DL control channel carries a DL assignment ineach DL subframe being associated with a certain UL control channelresource. In an exemplary case, ACK/NAKs from up to K DL subframes areto be bundled into one UL single subframe, i.e. the bundling windowcomprises K DL subframes. The DL subframes may be numbered from 1 to K.Within this set of subframes, the eNodeB can assign downlinktransmissions to a given a terminal. The number of assigned subframes,k′ can be between 0 and K.

Two examples are illustrated in FIG. 2. In the example, the number ofassociated DL subframes, K, is different for different subframes as wellas for different asymmetries. In FIG. 2 a the scenario of a 4DL: 1ULconfiguration is depicted. In this scenario the first (and only) ULsubframe in each half frame is associated to four DL subframes, i.e.K=4.

In FIG. 2 b, the scenario of a 3DL: 2UL configuration is depicted. Inthis scenario the first UL subframe in each half frame is associated totwo DL subframes, i.e. K=2, while the second UL subframe is associatedwith a single DL subframe, i.e. K=1.

As mentioned above the base station 110 transmits data in k′ subframesto the terminal. The terminal 120 at the receiver side will attempt todetect and decode DL assignments in each DL subframe. This makes itpossible for the terminal 120 to keep track of the number of detected DLassignments during a bundling window, denoted k. In some embodiments,the terminal 120 comprises a counter. For each DL subframe in which itreceives a DL assignment, the terminal 120 may increase the countercounting how many DL assignments it has received.

The terminal 120 will further attempt to decode the transport blocks inthe DL subframes in which it has detected a DL assignment and by meansof Cyclic Redundancy Check (CRC) estimate whether the transport block iscorrectly received or not. Now, the terminal 120 knows how manytransport blocks that were successfully received. CRC may also be usedfor detecting DL assignments.

In some embodiments, a Downlink Assignment Index (DAI) is signaled tothe terminal 120 from the base station 110 as part of the downlinkassignment in each DL subframe. The DAI represents the number ofprevious and/or minimum number of future assigned DL subframes withinthe bundling window. If such is signaled, the terminal 120 may furthercompare the counter on the number of received DL assignments with a DAIsignaled from the base station 110 to determine at least if any previousDL subframe has been missed or not.

When each one of the decoded transport block is correctly receivedwithin the k detected downlink subframes, a combined, or bundled encodedACK message for k subframes is provided from the terminal 120 to thebase station 110. The encoded ACK message also contains k, the number ofsubframes acknowledged. In the case of e.g. four different subframes,all being ACK, are represented as one combined ACK together with thenumber 4 to indicate that the ACK is valid for 4 subframes. The encodedACK message can be transmitted using Phase-Shift Keying (PSK) modulationin such a way that the used constellation point is also determined bythe number of received subframes in case a bundled ACK is transmitted.

When the terminal 120 detects for example using a DAI that a downlinkassignment has been missed, or when a transport block failed to bedecoded in any of the detected k subframes, a NAK message is provided tothe base station 110. Note that the same message is provided to the basestation independently of the number of received subframes. The NAKmessage may be modulated using PSK in such a way that constellationpoint that is different from the PSK constellation point that would havebeen used for modulating said ACK message for any k is used.

The base station 110 receives the transmitted message which can beeither NACK or ACK of k subframes, where k can be between 1 and K. Incase a NAK is received, the base station 110 knows that at least one outof the k′ transmitted subframes have not been correctly received. Thebase station 110 will therefore retransmit the k′ subframes accordingly.In case an ACK of k subframes is received by the base station 110, thebase station 110 can compare this with the number of assigned subframesk′ and if the received message does not agree with the number oftransmitted subframes, the base station 110 can detect that at least oneassignment has been completely missed and retransmit the correspondingsubframes.

In some embodiments and for the case where the terminal 120 knows it hasmissed all DL assignment, the terminal 120 may respond with a NAK inthis case. In some embodiments, the terminal 120 may choose to respondwith a Discontinuous Transmission (DTX) which means that no response isgiven.

According to some embodiments, the terminal 120 responds to the basestation 110 with at least one of K+1 messages representing:

-   -   NAK; for the case that at least one DL assignment was detected        and that the decoding of least one of the transport block        failed. It may also be generated for the case that no assignment        was detected but that the terminal still needs to transmit an        ACK/NAK, for example together with a scheduling request or a        Channel Quality Indicator CQI report. Furthermore, NAK may also        be generated for the case that the terminal 120 knows, for        example due to the use of DAI, that at least one assignment has        been missed.    -   ACK 1; for the case that one DL assignment was detected and that        the transport block(s) passed the decoding and CRC.    -   ACK 2; for the case that two DL assignments were detected and        that the transport block(s) passed the decoding and CRC, etc up        to:    -   ACK K; for the case that K DL assignments were detected and the        transport blocks passed the decoding and CRC.

In certain embodiments, the terminal 120 may choose to not respond (DTX)when the terminal 120 knows that at least one assignment has beenmissed, as enabled by the using of the DAI in the DL assignment (if suchis present). Furthermore, it may also choose to respond with NAK in thiscase. Nevertheless, there may in certain embodiments be an additionalmessage for DTX and there are then in total K+2 messages.

In further embodiments, less than K+1 (or K+2) messages are possible,and the meaning of different messages may then be slightly different.For example, with K=4 but only four different messages, (using QPSKmodulation, see below), the terminal 120 responds to the base station110 with at least one of the 4 messages representing for example:

-   -   NAK,    -   ACK1 or ACK4,    -   ACK 2, and    -   ACK 3,

or in another example:

-   -   NAK,    -   ACK 1,    -   ACK 2, and    -   ACK 3 or ACK 4,        or any other suitable combination.

In the embodiments where DAI is used, the base station 110 signals thenumber of previous and/or future assigned DL subframes within a bundlingwindow to the terminal 120. As mentioned above, the terminal 120 can,when it has received multiple DL assignments, count the number andcompare with the signaled number in the DAI to see whether it has missedany DL assignments.

In an alternative embodiment, which is suitable when a DAI is used, ACKk represents an ACK with subframe k, k=1, 2, . . . , K being the lastreceived subframe. Since the base station 110 knows the contents of theDAI in each and every DL subframe, it will hence know what the terminal120 based the bundled ACK/NAK on, if it knows which DL subframe was thelast received. Then, the DAI may be used by the terminal 120 to seewhether it missed any previous DL assignment, and by signaling the lastreceived DL subframe to the base station 110, it is possible for thebase station 110 to see whether any DL assignment was missed at the end.

In one embodiment, DAI represents the number of subframes beingscheduled so far to the terminal 120 in a bundling window. In anexemplary scenario, the base station 110 transmits four subframes, S1,S2, S3 and S4 in a bundling window to the terminal 120, and signals tothe terminal 120 that DAI is four in the last. If the terminal 120misses one or more subframes in the end of the bundling window, theterminal 120 will believe that it has received all subframes. In thesame way as mentioned above, the encoded ACK message may be modulatedsuch that the number of the last received subframe, k, is modulated intoa PSK constellation point. If receiving this ACK message, the basestation 110 will understand that the terminal 120 has missed anysubframe with a number above k and the base station 110 then retransmitsthe missed subframes to the terminal 120.

For example (A=correctly received, D=missed):

-   -   If S1-A, S2-A, S3-A, S4-D, the terminal 120 will provide the        base station 110 with an ACK 3, because subframe 3 was the last        correctly received subframe. The base station 110 will then        retransmit S4.    -   If S1-A, S2-A, S3-D, S4-D, the terminal 120 will provide the        base station 110 with an ACK 2, because subframe 2 was the last        correctly received subframe. The base station 110 will then        retransmit S3 and S4.    -   If S1-A, S2-D, S3-D, S4-D, the terminal 120 will provide the        base station 110 with an ACK 1, because subframe 1 was the last        correctly received subframe. The base station 110 will then        retransmit S2, S3 and S4.

In the case when a subframe is missed not being in the end of thebundling window, the terminal 120 transmits an encoded NAK message tothe base station 110. The encoded NAK message is modulated into a PSKconstellation point being different from the PSK constellation pointthat would have been used for modulating an ACK message, in the same wayas being described above. This will e.g. occur for the scenarios when:

-   -   S1-A, S2-D, S3-A, S4-A, or when    -   S1-A, S2-D, S3-D, S4-A, or when    -   S1-D, S2-A, S3-A, S4-A, etc.

In this case the base station 110 will not know which subframes thatwere not received by the terminal 120. The base station 110 maytherefore retransmit all subframes S1, S2, S3 and S4 within the bundlingwindow.

A scheduler in the base station 110 may schedule several terminals inthe same subframes (inclusive the terminal 120), and as mentioned above,in some embodiments keep track of how many and which DL subframe theterminal 120 has been assigned resources in. By inspection of the HARQfeedback, it will know whether the transmissions within the bundlingwindow were successful or not.

In some embodiments, a bundled ACK/NAK is transmitted from the terminal120 to the base station 110 on PUCCH together with a Scheduling Request(SR) or a CQI report, or in general when the PUCCH resource can carry aPSK, then the modulation alphabet used can be taken as K+1 PSK. Thefollowing formula may be used:

S _(—) k=exp(j*2*π/(K+1)*k), k=0,1, . . . K

wherein j=sqrt(−1), K is the total number of possible subframes in thebundling window, i.e. not scheduled but possible to schedule, and k isthe number of subframes being acknowledged in one encoded ACK message.S_k is the modulated symbol that is transmitted from the terminal 120.Some examples of PSK constellations are given in FIGS. 3 a, b and c, ofwhich FIG. 3 b depicts a PSK constellation using this formula.

FIG. 3 a shows a non-uniform PSK constellation wherein ACK1 and ACK2 isplaced further away from NAK then from each other to be able have ahigher requirement on NAK->ACK error then on ACK1->ACK2 error.

FIG. 3 b shows a uniform PSK constellation wherein ACK1, ACK2, ACK3 andNAK are placed in a Quadrature Phase Shift Keying (QPSK) constellation.As QPSK is normally used for data hence it is easier for the basestation 110 or the terminal 120 not having a special constellationACK/NAK feedback. It may also be possible to reuse some of theimplemented software or hardware when reading out the symbols or writingthem in the base station 110 and the terminal 120 as the same mappingfunction is used for data.

FIG. 3 c shows a non-uniform PSK constellation depicting different PSKconstellation points for ACK1, ACK2, ACK3, ACK4 and NAK wherein ACK1 andACK2 are placed further away from NAK then from each other to be ablehave a higher requirement on NAK->ACK error then on ACK1->ACK2 error.The ACK3 and ACK4 may be placed closer to NAK since it is not so likelythat all 3 or 4 subframes will be missed at the same time theACK3->ACK2, ACK4->ACK1 will not be set to a minimum.

Regarding the error requirements, in terms of Pr(DTX->ACK), i.e. that amissed assignment is misinterpreted as ACK, is higher or much higherthan the corresponding requirement on Pr(NAK->ACK), i.e. that a NAK ismisinterpreted as ACK. For example, the probability Pr(DTX->ACK) whichrepresents the error probability that a missed DL assignment isinterpreted as an acknowledgement is of the order 0.01-0.1 whereas theprobability Pr(NAK->ACK) which represents the probability that a NAK isinterpreted as an ACK is of the order 0.0001-0.001. The encoding of themessages may then be done so to exploit this. For this purpose, analternative embodiment is to do the encoding using non-uniform K+1 PSKwhere the distance between NAK and the closest ACK point(s) is largerthan the smallest distance between any two ACK points. This means that

min_(i)P(NAK->ACK_(—) i)<min_(j,k)P(ACK_(—) j->ACK_(—) k)

The probability of any transmitted ACK messages being interpreted as aNAK is to be lower than the probability that the number of ACKs ismisinterpreted. The above expression represents that a specific numberof ACK subframes from the terminal 120 being misinterpreted as anothernumber of ACK subframes in the base station 110, so that the error ofNAK being decoded as any of the ACKs is smaller than any error eventthat one ACK is decoded as another ACK. Some examples are shown in FIGS.4 a, b and c.

FIG. 4 a shows a non-uniform PSK constellation for ACK1, ACK2 and NAK,using similar principle as illustrated in FIG. 3 a but even moreprotection for the NAK->ACK error.

FIG. 4 b shows a non-uniform PSK constellation for ACK1. ACK2. ACK3 andNAK using similar principle as illustrated in FIG. 4 a but beingextended to 3 ACKs.

FIG. 4 c shows a non-uniform PSK constellation for ACK1, ACK2, ACK3,ACK4 and NAK using similar principle as illustrated in FIG. 4 a butbeing extended to 4 ACKs

In some embodiments, QAM constellations can be used instead of a PSK,such as e.g. 16QAM, FIG. 5 shows a constellation wherein ACK1 and ACK2(the same constellation point), ACK3, ACK4, ACK5, ACK6, ACK7, ACK8,ACK9, ACK10, ACK11, ACK12, ACK13, ACK14, ACK15, ACK16 and NAK are placedin a 16QAM constellation, which e.g. may be used in LTE advanced. In amore practical setting only a subset of the 16 constellation points areused with distances chosen so as to meet the different target errorprobabilities.

Thus, a major benefit of the invention is that the signalling isreduced. Instead of signalling log(2K) bits which is required to conveyinformation on both ACK/NAK and the number of received subframes, onlylog(K+1) bits can be used since the number of subframes is only encodedwhen an ACK is transmitted.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive.

It is to be noted that although terminology from 3GPP LTE has been usedin this disclosure to exemplify the invention, this should not be seenas limiting the scope of the invention to only the aforementionedsystem. Other wireless systems, including LTE-Adv, WCDMA, WiMax. UMB andGSM, as well as future wireless systems, may also benefit fromexploiting the ideas covered within this disclosure.

The method steps in the terminal 120 for providing an ACK/NAK message tothe base station 110 according to some embodiments will now be describedwith reference to a flowchart depicted in FIG. 6. As mentioned above,the base station 110 and the terminal 120 are comprised in atelecommunications system. The method comprises the steps of:

601. The terminal 120 counts the number of assigned downlink subframesdetected from the base station 110 resulting in k. 602. The terminal 120then establishes whether each of a number of transport blocks comprisedin the counted k downlink subframes is correctly received or not. 603.When each one of the transport blocks, comprised in the k downlinksubframes is estimated as correctly received, the terminal 120 providesto the base station 110 an encoded ACK message for the k subframes. TheACK message comprises k, the number of subframes. The encoded ACKmessage may be modulated such that the constellation point is selecteddepending on k, the number of subframes being acknowledged. 604. Whenany of the transport blocks comprised in the number k downlink subframesis estimated as not correctly received, the terminal 120 may provide oneencoded NAK message for the k subframes bundled to the base station 110.The encoded NAK message may be modulated using a PSK constellation pointthat is different from the PSK constellation point that would have beenused for modulating said ACK message. 605. This is an optional step. Insome embodiments, the terminal 120 may obtain a Downlink AssignmentIndex “DAI” from the base station 110. In these embodiments, the DAI mayrepresent the number of previous and future assigned DL subframes. 606.This step is optional. In some embodiments the terminal 120 establishesif any DL subframes transmitted from the base station 110 has beenmissed. In some embodiments where a DAI was obtained in step 605 theterminal 120 compares the number of received DL assignments with the DAIsignalled from the base station 110 to determine if any previous DLsubframe has been missed or not 607. This step is optional. When a DLsubframe transmitted from the base station 110 has been established tobe missed, the terminal 120 may provide to the base station 110 oneencoded NAK message. The encoded NAK message is modulated into a PSKconstellation point being different from the PSK constellation pointthat would have been used for modulating said ACK message. 608. Thisstep is optional and an alternative to step 607. When all DL subframestransmitted from the base station 110 has been established to be missed,the terminal 120 may provide a response to the base station 110 with aDiscontinuous Transmission “DTX”. 609. This step is optional and analternative to step 607 and 608. When all DL subframes transmitted fromthe base station 110 has been established to be missed, the terminal 120may provide one encoded DTX message to the base station 110. The encodedDTX message may be modulated into a PSK constellation point beingdifferent from the PSK constellation point that would have been used formodulating said ACK message.

In some embodiments, the terminal 120 uses PSK comprising multiple PSKconstellation points. In some of these embodiments, the terminal 120uses a first constellation point NAK of the multiple PSK constellationpoints when transmitting the encoded NAK message, and different secondconstellation points ACK1, ACK2. ACK3. ACK4 of the multiple PSKconstellation points when transmitting the encoded ACK message fordifferent values of k. The different second constellation points ACK1,ACK2, ACK3, and ACK4 are all different from the first constellationpoint NAK and where the selected constellation points may depend on thenumber of received subframes k.

In some embodiments, uniform PSK is used for transmitting the encodedACK message for k subframes, or NAK message, or DTX message into a PSKconstellation point.

In some alternative embodiments, Quadrature Phase Shift Keying “QPSK” isused for transmission of the respective encoded ACK message for ksubframes, or NAK message, or DTX message.

In a specific alternative embodiment the terminal 120 uses QPSKcomprising, a first QPSK constellation point, a second QPSKconstellation point, a third QPSK constellation point and a fourth QPSKconstellation point. In this embodiment, the terminal 120 uses the firstconstellation point when modulating the encoded NAK message, the secondconstellation point when modulating the encoded ACK message for ksubframes when k=1 or 4, the third constellation point when modulatingthe encoded ACK message for k subframes when k=2, and the fourthconstellation point when modulating the encoded ACK message for Ksubframes when k=3.

In a specific embodiment the terminal uses X-QAM for modulating theencoded ACK message for k subframes, or NAK message, or DTX message intoan X-QAM constellation point. X can take on any of 2̂2, 2̂3, 2̂4, . . . 2̂N.

In some embodiments the terminal 120 uses non-uniform PSK for modulatingthe encoded ACK message for K subframes, or NAK message, or DTX messageinto a PSK constellation point.

To perform the method steps above for providing an ACK/NAK message tothe base station 110, the terminal 120 comprises an arrangement 700depicted in FIG. 7. As mentioned above, the base station 110 and theterminal 120 are comprised in a telecommunications system.

The terminal arrangement 700 comprises a counting unit 710 configured tocount the number of assigned downlink subframes detected from the basestation 110 resulting in k.

The terminal arrangement 700 further comprises an establishing unit 720configured to establish whether each of a number of transport blockscomprised in the counted k downlink subframes is correctly received ornot. The establishing unit 720 may further be configured to establish ifany DL subframes transmitted from the base station 110 has been missed.

The terminal arrangement 700 further comprises a sending unit 730configured to provide to the base station 110, an encoded ACK messagefor the k subframes. The ACK message comprises k, the number ofsubframes, when each one of the transport blocks, comprised in the kdownlink subframes is estimated as correctly received. The encoded ACKmessage may be modulated such that the constellation point is selecteddepending on k, the number of subframes being acknowledged.

The sending unit 730 is further configured to provide to the basestation 110 one encoded NAK message for the k subframes bundled, whenany of the transport blocks comprised in the number k downlink subframesis estimated as not correctly received. The encoded NAK message may bemodulated using a PSK constellation point being different from the PSKconstellation point that would have been used for modulating said ACKmessage.

In some embodiments the sending unit 730 is further configured toprovide one encoded NAK message to the base station 110 when a DLsubframe transmitted from the base station 110 has been established tobe missed. The encoded NAK message is modulated into a PSK constellationpoint being different from the PSK constellation point that would havebeen used for modulating said ACK message.

In an alternative embodiment, the sending unit 730 may further beconfigured to provide a response to the base station 110 with aDiscontinuous Transmission “DTX”, when all DL subframes transmitted fromthe base station 110 has been established to be missed.

In a further alternative embodiment the sending unit 730 is furtherconfigured to provide to the base station 110 one encoded DTX messagewhen all DL subframes transmitted from the base station 110 has beenestablished to be missed. The encoded DTX message is modulated into aPSK constellation point being different from the PSK constellation pointthat would have been used for modulating said ACK message.

In some embodiments, the terminal 120 is adapted to use PSK comprisingmultiple PSK constellation points. In some of these embodiments theterminal 120 is adapted to use a first constellation point NAK of themultiple PSK constellation points when transmitting the encoded NAKmessage, and a different second constellation points ACK1, ACK2, ACK3,ACK4 of the multiple PSK constellation points when transmitting theencoded ACK message for different values of k. The different secondconstellation points ACK1, ACK2, ACK3, and ACK4 may all be differentfrom the first constellation point NAK and the selected constellationpoints may depend on the number of received subframes k.

The terminal arrangement 700 may further comprise a receiving unit 730configured to obtain a DAI from the base station 110. The DAI representsthe number of previous and future assigned DL subframes. In theseembodiments, the establishing unit 720 may further be configured tocomparing the number of received DL assignments with the DAI signaledfrom the base station 110 to determine if any previous DL subframe hasbeen missed or not.

In some embodiments, uniform PSK is adapted to be used for modulatingthe encoded ACK message for K subframes, or NAK message, or DTX messageinto a PSK constellation point.

In some embodiments Quadrature Phase Shift Keying QPSK is adapted to beused for the respective encoded ACK message for k subframes, or NAKmessage, or DTX message transmitted by the terminal 120.

In a specific embodiments the terminal 120 is adapted to use QPSKcomprising, a first QPSK constellation point, a second QPSKconstellation point, a third QPSK constellation point and a fourth QPSKconstellation point. In this embodiment the terminal 120 is adapted touse the first constellation point when modulating the encoded NAKmessage, the second constellation point when modulating the encoded ACKmessage for k subframes when k=1 or 4, the third constellation pointwhen modulating the encoded ACK message for k subframes when k=2, andthe fourth constellation point when modulating the encoded ACK messagefor k subframes when k=3.

In some embodiments X-QAM is used for modulating the encoded ACK messagefor k subframes, or NAK message, or DTX message into a X-QAMconstellation point, where X can take on any of 2̂2, 2̂3, 2̂4, . . . 2̂N.

In some embodiments non-uniform PSK is adapted to be used for modulatingthe encoded ACK message for k subframes, or NAK message, or DTX messageinto a PSK constellation point.

The method steps in the base station 110, for handling anacknowledgement ACK/NAK report from a terminal 120, according to someembodiments will now be described with reference to a flowchart depictedin FIG. 8. As mentioned above the base station 110 and the terminal 120are comprised in a telecommunications system. The method comprises thesteps of:

801. The base station110 sends a number of downlink subframes comprisingtransport blocks to the terminal 120. 802. When each one of thetransport blocks, comprised in the k downlink subframes is estimated ascorrectly received by the terminal 120, the base station receives oneencoded ACK message for k subframes from the terminal 120. The encodedACK message comprises k, the number of subframes detected by theterminal 120. The terminal 120 has counted the received subframesresulting in the number k. The encoded ACK message may be modulated suchthat the constellation point is selected depending on k, the number ofsubframes being acknowledged. 803. When any of the transport blockscomprised in the number k downlink subframes is estimated by theterminal 120 as not correctly received, the base station 110 may receivefrom the terminal 120 one encoded NAK message for the k subframesbundled. The encoded NAK message may be modulated using a PSKconstellation point being different from the PSK constellation pointthat would have been used for modulating said ACK message. 804. This isan optional step. In some embodiments the base station 110 signals DAIto the terminal 120: The DAI represents the number of previous andfuture assigned DL subframes. The DAI will be used by the terminal 120for establishing if any downlink subframes transmitted from the basestation 110 has been missed, by comparing the number of receiveddownlink assignments with the DAI signalled from the base station 110.805. This is an optional step. When a downlink subframe transmitted fromthe base station 110 to the terminal 120 has been established to bemissed by the terminal 120, the base station 110 may receive one encodedNAK message from the terminal 120. The encoded NAK message is modulatedinto a PSK constellation point is different from the PSK constellationpoint that would have been used for modulating said ACK message. 806.This is an optional step. When all the K DL subframes transmitted fromthe base station 110 to the terminal 120 has been established to bemissed by the terminal 120, the base station 110 may receive a responsefrom the terminal 120 with a Discontinuous Transmission DTX. 807. Thisis also an optional step. When all the DL subframes transmitted from thebase station 110 to the terminal 120 has been established to be missedby the terminal 120, the base station 110 may receive from the terminal120 one encoded DTX message. The encoded DTX message is modulated into aPSK constellation point being different from the PSK constellation pointthat would have been used for modulating said ACK message.

In some embodiments, PSK comprising multiple PSK constellation pointsare used in the received ACK/NAK message. In these embodiments a firstconstellation point NAK of the multiple PSK constellation points is usedfor transmitting the encoded NAK message, and different secondconstellation points ACK1, ACK2, ACK3, ACK4 of the multiple PSKconstellation points is used for transmitting the encoded ACK messagefor different values of k. The different second constellation pointsACK1, ACK2, ACK3, and ACK4 may all be different from the firstconstellation point NAK and the selected constellation points maydepends on the number k.

In some embodiments uniform PSK is used for modulation of the encodedACK message for k subframes, or NAK message, or DTX message into a PSKconstellation point.

In some embodiments QPSK is used for the respective encoded ACK messagefor k subframes, or NAK message, or DTX message transmitted by theterminal 120.

In some further embodiments QPSK is used comprising a first QPSKconstellation point, a second QPSK constellation point, a third QPSKconstellation point and a fourth QPSK constellation point. In theseembodiments the first constellation point is used for transmitting theencoded NAK message, the second constellation point is used formodulation in the encoded ACK message for k subframes when k=1 or 4, thethird constellation point is used for modulation in the encoded ACKmessage for K subframes when k=2, and the forth constellation point isused for modulation in the encoded ACK message for k subframes when k=3.

In some alternative embodiments X-QAM may be used for modulating theencoded ACK message for k subframes, or NAK message, or DTX message intoa X-QAM constellation point, where X can take on any of 2̂2, 2̂3, 2̂4, . .. 2̂N.

In some alternative embodiments non-uniform PSK is used for modulationof the encoded ACK message for k subframes, or NAK message, or DTXmessage into a PSK constellation point.

To perform the method steps above for handling an acknowledgementACK/NAK message from a terminal 120, the base station 110 comprises anarrangement 900 depicted in FIG. 9. As mentioned above, the base station110 and the terminal 120 are comprised in a telecommunications system.

The base station arrangement 900 comprises a sending unit 910 configuredto send a number of downlink subframes comprising transport blocks tothe terminal 120.

The sending unit 910 may further be configured to signal a DAI to theterminal 120. The DAI represents the number of previous and futureassigned DL subframes, which DAI is adapted to be used by the terminal120 for establishing if any DL subframes transmitted from the basestation 110 has been missed, by comparing the number of received DLassignments with the DAI signaled from the base station 110.

The base station arrangement 900 further comprises a receiving unit 920configured to receive from the terminal 120 one encoded ACK message fork subframes, which encoded ACK message comprises k, the number ofsubframes detected by the terminal 120, when each one of the transportblocks, comprised in the k downlink subframes is estimated as correctlyreceived by the terminal 120. The encoded ACK message may be modulatedsuch that the constellation point is selected depending on k, the numberof subframes being acknowledged.

The receiving unit 920 is further configured to receive from theterminal 120 one encoded NAK message for the k subframes bundled, whenany of the transport blocks comprised in the number k downlink subframesis estimated by the terminal 120 as not correctly received. The encodedNAK message may be modulated using a PSK constellation point beingdifferent from the PSK constellation point that would have been used formodulating said ACK message.

The receiving unit 920 may further be configured to receive a responsefrom the terminal 110 with a Discontinuous Transmission DTX, when allthe k DL subframes transmitted from the base station 110 to the terminal120 has been established to be missed by the terminal 120.

The receiving unit 920 may further be configured to receive from theterminal 120 one encoded DTX message when all the DL subframestransmitted from the base station 110 to the terminal 120 has beenestablished to be missed by the terminal 120. The encoded DTX message ismodulated into a PSK constellation point being different from the PSKconstellation point that would have been used for modulating said ACKmessage.

In some embodiments PSK comprising multiple PSK constellation points isadapted to be used in the received ACK/NAK message. In these embodimentsa first constellation point NAK of the multiple PSK constellation pointsis adapted to be used for the encoded NAK message, and a differentsecond constellation points ACK1, ACK2, ACK3, ACK4 of the multiple PSKconstellation points is adapted to be used for the encoded ACK messagefor different values of k. The different second constellation pointsACK1, ACK2, ACK3, and ACK4 may all be different from the firstconstellation point NAK and the selected constellation points may dependon the number k.

In some embodiments uniform PSK is used for modulation of the encodedACK message for k subframes, or NAK message, or DTX message into a PSKconstellation point.

In some embodiments QPSK is used for the respective encoded ACK messagefor k subframes, or NAK message, or DTX message, transmitted by theterminal 120.

In some further embodiments QPSK is used comprising a first QPSKconstellation point, a second QPSK constellation point, a third QPSKconstellation point and a fourth QPSK constellation point. In theseembodiments the first constellation point is used for modulation in theencoded NAK message, the second constellation point is used formodulation in the encoded ACK message for k subframes when k=1 or 4, thethird constellation point is used for modulation in the encoded ACKmessage for k subframes when k=2, and the forth constellation point isused for modulation in the encoded ACK message for k subframes when k=3.

In some alternative embodiments X-QAM may be used for modulating theencoded ACK message for K subframes, or NAK message, or DTX message intoa X-QAM constellation point, where X can take on any of 2̂2, 2̂3, 2̂4, . .. 2̂N.

In some alternative embodiments non-uniform PSK is used for modulationof the encoded ACK message for K subframes, or NAK message, or DTXmessage into a PSK constellation point.

The present mechanism for above for handling an acknowledgement ACK/NAKreport, may be implemented through one or more processors, such as aprocessor 740 in the terminal arrangement 700 depicted in FIG. 7 or theprocessor 930 in the base station arrangement 900 depicted in FIG. 9,together with computer program code for performing the functions of thepresent solution. The program code mentioned above may also be providedas a computer program product, for instance in the form of a datacarrier carrying computer program code for performing the presentsolution when being loaded into the base station 110 or the terminal120. One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code can furthermore be provided as pure program code on aserver and downloaded to the base station 110 or the terminal 120remotely.

When using the word “comprise” or “comprising” it shall be interpretedas non-limiting, i.e. meaning “consist at least of”.

The present invention is not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

1. An arrangement in a base station for handling anacknowledgement/not-acknowledgement (ACK/NAK) message from a terminal,the base station and the terminal in a telecommunication system, thearrangement comprising: a sending unit configured to send a number ofdownlink subframes including transport blocks to the terminal and tosignal to the terminal in each downlink subframe a downlink assignmentindex (DAI) that represents a number of previous assigned downlinksubframes and that enables the terminal to establish if any downlinksubframe transmitted by the base station has been missed by comparing anumber k of received downlink assignments with a DAI; and a receivingunit configured to receive from the terminal for the k downlinkassignments one encoded ACK message that includes k, the number ofdownlink assignments detected by the terminal, when each transport blockin the downlink subframes in which the terminal has detected a downlinkassignment is estimated as correctly received by the terminal, whereinthe receiving unit is further being configured to receive from theterminal one encoded NAK message that is modulated into a constellationpoint that is different from a constellation point into which the ACKmessage would have been modulated when a downlink assignment transmittedby the base station to the terminal has been established to be missed bythe terminal, wherein the receiving unit is further configured toreceive the encoded ACK message modulated such that the constellationpoint depends on k, the number of subframes being acknowledged, and toreceive the encoded NAK message modulated using a constellation pointdifferent from the constellation point that would have been used formodulating the ACK message, and wherein a received ACK/NAK message usesquadrature phase-shift keying (QPSK) modulation including a first QPSKconstellation point, a second QPSK constellation point, a third QPSKconstellation point, and a fourth QPSK constellation point; the firstQPSK constellation point is used for the encoded NAK message; the secondQPSK constellation point is used for the encoded ACK message for kdownlink assignments when k=1 or k=4; the third QPSK constellation pointis used for the encoded ACK message for k downlink assignments when k=2;and the fourth QPSK constellation point is used for the encoded ACKmessage for k downlink assignments when k=3.